As written above, in his sealed cat form he's identical to Nyanko-sensei except for his coloring, but in his normal state he looks very humanoid, except he has blue eyes and hair and being extremely large, with a wingspan twice as tall as he is. He wears a white yukata with nothing underneath and no footwear.
When he first appears as a black maneki neko he doesn't speak, but when he's released from the sealed form we learn that he's a soft spoken and kind Ayakashi. The other ayakashi look up to him, because he gave them power to be able to live in the forest in peace, though they think of him as a bit soft in the head for befriending humans. He apparently likes humans, and sounded very sad when he learned that his friend had died long ago and decides to never go human settlements ever again to make sure none of his underlings attempt to attack the humans for his sake again.
Ichiban Kuji Natsume Yuujinchou ~Nyanko-sensei wa Kuishinbou~: Riou
Rating: 4 | Comments: 0
Ichiban Kuji Natsume Yuujinchou Tribute Gallery ~Enmusubi Monogatari~: Riou Chibi Kyun-Chara
PVC, ABS, Banpresto
Rating: 1 | Comments: 0
Natsume Yuujinchou Bendable Charm: Nyanko-sensei Black Nyanko Ver.
Rubber, Metal, Unknown
Rating: 0 | Comments: 0
Natsume Yujincho Yura-Yura Clip Collection Vol.2: Riou (Black Nyanko)
Stainless Steel, Steel, Sol International
Rating: 6 | Comments: 0